Modifying PVDF membranes with Al₂O₃ nanoparticles via two methods provided a new idea for removing dyes. It also elucidatend the retention mechanism of the modified membranes when treating different dye solutions.

Methyl-modified niobium-doped silica (Nb/SiO₂) materials with various Nb/Si molar ratios (n_Nb) were fabricated using tetraethoxysilane and methyltriethoxysilane as the silica source and niobium pentachloride as the niobium source by the sol–gel method, and the Nb/SiO₂ membranes were prepared thereof by the dip-coating process under an N₂ calcining atmosphere. Their microstructures were characterized and gas permeances tested. The results showed that the niobium element existed in the formation of the Nb-O groups in the Nb/SiO₂ materials. When the niobium doping content and the calcining temperature were large enough, the Nb₂O₅ crystals could be formed in the SiO₂ frameworks. With the increase of n_Nb and calcination temperature, the formed particle sizes increased. The doping of Nb could enhance the H₂/CO₂ and H₂/N₂ permselectivities of SiO₂ membranes. When n_Nb was equal to 0.08, the Nb/SiO₂ membrane achieved a maximal H₂ permeance of 4.83 × 10⁻⁶ mol·m⁻²·Pa⁻¹·s⁻¹ and H₂/CO₂ permselectivity of 15.49 at 200 °C and 0.1 MPa, which also exhibited great hydrothermal stability and thermal reproducibility.

Akhtenskites merely remove NH₄⁺ by adsorption, but remove Mn²⁺ by adsorption and catalytic oxidation simultaneously. The removal efficiency and crystal structure are obviously affected by the structure cations.

Iron-manganese co-oxide film (MeO_x) has a high removal efficiency for ammonium (NH₄⁺) and manganese (Mn²⁺) in our previous studies, but it cannot effectively remove COD_Mn from water. In this study, the catalytic oxidation ability of MeO_x was enhanced by dosage with potassium ferrate (K₂FeO₄) to achieve the simultaneous removal of COD_Mn and NH₄⁺ from water in a pilot-scale experimental system. By adding 1.0 mg/L K₂FeO₄ to enhance the activity of MeO_x, the removal efficiencies of COD_Mn (20.0 mg/L) and NH₄⁺ (1.1 mg/L) were 92.5 ± 1.5% and 60.9 ± 1.4%, respectively, and the pollutants were consistently and efficiently removed for more than 90 days. The effects of the filtration rate, temperature and pH on the removal of COD_Mn were also explored, and excessive filtration rate (over 11 m/h), lower temperature (below 9.2 °C) and pH (below 6.20) caused a significant decrease in the removal efficiency of COD_Mn. The removal of COD_Mn was analyzed at different temperatures, which proved that the kinetics of COD_Mn oxidation was pseudo-first order. The mature sands (MeO_x) from column IV were taken at different times for microscopic characterization. Scanning electron microscope (SEM) showed that some substances were formed on the surface of MeO_x and the ratio of C and O elements increased significantly, and the ratio of Mn and Fe elements decreased significantly on the surface of MeO_x by electron energy dispersive spectrometer (EDS). However, the elemental composition of MeO_x would gradually recover to the initial state after the dosage of Mn²⁺. According to X-ray photoelectron spectroscopy (XPS) analysis, the substance attached to the surface of MeO_x was [(-(CH₂)₄O-)_n], which fell off the surface of MeO_x after adding Mn²⁺. Finally, the mechanism of K₂FeO₄-enhanced MeO_x for COD_Mn removal was proposed by the analysis of the oxidation process.

Mn²⁺ is a prevalent contaminant in groundwater. In this study, manganese oxides (MnO_x) were prepared via a redox method to remove Mn²⁺ from water. The effects of the drying operation in the preparation process, including heat drying at 20–120 °C with different times and freeze drying methods, on the structural properties, manganese removal performance and mechanisms were investigated. The results indicate that the drying conditions can significantly affect the removal performance and stability of MnO_x. The MnO_x dried at 50 °C for 12 h exhibited the best Mn²⁺ removal efficiency and stability, with an adsorption capacity of 125.7 mg/g and removal efficacy of 95.1% after six reuse cycles. The removal pathway experiments revealed that the sample dried at 50 °C for 12 h had superior catalytic oxidation abilities for Mn²⁺, while other samples removed Mn²⁺ by primarily relying on the adsorption process. The investigation of the structure revealed that excessive heat drying led to the shrinkage of the oxide particles, a reduction in the surface voids, and a decrease in the hydroxyl groups. Conversely, insufficient drying time or temperatures resulted in high water content in MnO_x, which occupied the surface active sites. The XPS analysis indicated that the catalytic oxidation of Mn²⁺ primarily relied on Mn(III) and adsorbed oxygen on the surface of MnO_x. With freeze drying or inadequate heat drying, a large amount of Mn(II) remained on the oxide surface, and the over-drying operation resulted in excessive conversion from Mn(II) to Mn(IV), reducing the catalytic activity and resulting in low removal stability.